Production of bioflocculants from spent brewer's yeast and its application in the treatment of effluents with textile dyes
Graphical abstract
Introduction
The textile industry is known as one of the most water-consuming sectors [1]. It is estimated that a quantity near 100 L of water is required for dyeing and washing single jeans pants [2]. This high-water demand is summed with the presence of a diverse range of compounds that are involved in the industry's inner processes. Persistent color, toxicity, and low degradability are relevant characteristics of dye-containing wastewaters that can further constrain the efficacy of conventional biological treatment approaches [3]. The inappropriate disposal of these wastewaters may interfere with aquatic ecosystems, by reducing photosynthesis capacity and turning water unsuitable for the human supply [4].
Several techniques have been employed for textile wastewater clarification and decontamination. Advanced oxidative process [5], adsorption [6], ultrafiltration [7], and electrocoagulation [2] are some examples of recently employed methodologies that present high efficiency on dye degradation/separation but are still associated with high-cost treatment systems for industrial wastewaters. Flocculation and coagulation are cost-effective treatment systems that present efficiency in the industrial field. However, some inorganic and synthetic flocculating agents have been related to environmental and human health concerns [8], [9]. Bioflocculants are an eco-friendly alternative once it is constituted by natural components, mainly carbohydrates and proteins, from microorganisms. According to Artifon et al. [10], studies that report the application of bioflocculants on dye-containing wastewaters treatment have increased in recent years. Sun et al. [11] produced polymeric substances by hydrolyzing periphytic biofilms and obtained 56 % of decolorization in aniline blue solution. Color removal outcomes higher than 80 % are reported by Saha et al. [12] when applying extracellular substances from several microorganisms cultivation medium on congo red dye system. However, the relatively low extracellular polymeric substances content released by pure culture strains imposes constraints on the application of these substances on a wide scale [11]. On the other hand, the extraction of biopolymer components from microbial aggregates, such as industrial residues, implies high bioflocculant yield and low-cost requirements [10].
The spent brewer's yeast is a residue of the brewing industry that has attracted interest due to its rich chemical composition [13], [14]. In the fermentation process, the growth of biomass yields an average ratio of 2.0 kg of yeast (dry weight) per ton of beer produced [15]. After brewing spent grain, the spent brewer's yeast is considered the second-largest byproduct in this industry [16]. These facts highlight the huge amount of wet biomass generated and the demand for proper management of this residue. Traditionally, its applications have comprehended mainly animal and human nutrition [17], but different applications focused on the valorization of spent brewer's yeast into other components of interest are becoming significant [18]. Biopolymer [15] and added-value molecules recovery [13], bioactive peptides source [19], and flocculant for algae harvesting font [20], are some recent applications related to this brewing residue. In this sense, this work milestone is to feature a bioflocculant produced by the spent brewer's yeast from the brewing industry and, for the first time, evaluate its flocculating potential in the dye-containing textile industry wastewaters treatment.
Section snippets
Source of materials
The spent brewer's yeast was donated by a local brewing industry after the fermentation process. The collected biomass was washed twice with distilled water, concentrated to 30 % (wt/wt) at 60 °C, and kept at 4 °C awaiting experiments.
The produced bioflocculant was tested in two different textile wastewaters systems containing dispersive dyes from TMX (Brazil). The first was a real effluent from a washing bath obtained from a local textile industry containing rhodamine trillon FRBT (OD520 nm)
Bioflocculant extraction
Table 2 presents the experimental results of color removal from a full 23 factorial design. These outcomes were statistically analyzed to evaluate the effects of each variable on the flocculation activity of the resulting bioflocculant. A quadratic model (Eq. (2)) was proposed to describe experimental data and all linear and quadratic terms were statistically significant (p < 0.5). The proposed model was validated by analysis of variance (ANOVA) as presented in Table 3.
Conclusions
The spent brewer's yeast is a valuable resource of biological substances that deserves valorization. In this study, the alkaline hydrolysis of the yeast cell showed to be a promising pathway to release inner polymeric substances that can be applied in several fields. The bioflocculant produced possesses efficiency on flocculation activity without cation further addition and, at acid pH, precipitates two potential recalcitrant dyes, rhodamine and flavine. Although the presence of the
Declaration of competing interest
The authors declare that they have no conflict of interest.
Acknowledgments
The authors acknowledge CAPES and CNPq for financial support and scholarships. The authors are also grateful to LABSIN-LABMASSA – Mass Transfer Laboratory and CORATEX Company for the infrastructure provided.
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